The present invention relates to a dimmer for use with vehicle which controls the intensity of a light source for illuminating, at night or the like, various meters such as a speedmeter, a fuel gauge, etc. mounted on the dashboard of an automobile, or a displaying light source which constitutes said meters and indicators themselves.
If the light source mounted on the dash-board of the automobile as described above is too bright, the eyes of a driver directly catch the light therefrom, or the light therefrom is reflected by a window to produce a reflection on the window to dazzle the driver, which is unfavorable for safety driving. Such a phenomenon is particularly liable to occur at night when a difference between circumambient brightness and brightness of light source is great. Therefore, a dimmer has been heretofore provided on the automobile so as to suitably control the brightness of these light sources to meet the circumambient conditions.
However, in the conventional dimmer of this kind, the duty ratio of output pulses of a pulse generator, which generates pulses at fixed frequency, is controlled by varying the resistance of a manually operable variable resistor. Therefore, even during the driving, the dimming operation had to be carried out by manual control of the variable resistor as the occasion demands.